Make aborted commits inform the scroll delegate.

cc/layers/layer_impl.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/layers/layer_impl.h"
 
 #include "base/debug/trace_event.h"
 #include "base/debug/trace_event_argument.h"
 #include "base/json/json_reader.h"
 #include "base/strings/stringprintf.h"
@@ skipping 384 matching lines @@
   return (orientation == HORIZONTAL) ? user_scrollable_horizontal_
                                      : user_scrollable_vertical_;
 }
 
 void LayerImpl::ApplySentScrollDeltasFromAbortedCommit() {
   // Pending tree never has sent scroll deltas
   DCHECK(layer_tree_impl()->IsActiveTree());
 
   // Apply sent scroll deltas to scroll position / scroll delta as if the
   // main thread had applied them and then committed those values.
-  //
-  // This function should not change the total scroll offset; it just shifts
-  // some of the scroll delta to the scroll offset.  Therefore, adjust these
-  // variables directly rather than calling the scroll offset delegate to
-  // avoid sending it multiple spurious calls.
-  //
-  // Because of the way scroll delta is calculated with a delegate, this will
-  // leave the total scroll offset unchanged on this layer regardless of
-  // whether a delegate is being used.
-  scroll_offset_ += gfx::ScrollOffset(sent_scroll_delta_);
-  scroll_delta_ -= sent_scroll_delta_;
-  sent_scroll_delta_ = gfx::Vector2dF();
+  SetScrollOffsetAndDelta(
+      scroll_offset_ + gfx::ScrollOffset(sent_scroll_delta_),
+      ScrollDelta() - sent_scroll_delta_);

[bokan, 2014/10/29 23:55:42]

SetScrollOffsetAndDelta sets the unsent delta on the twin layer in the pending
tree, will that now remove the sent delta twice?

[aelias_OOO_until_Jul13, 2014/10/30 01:46:55]

Empirically I don't see any bugs if I try scrolling on continuously invalidating
pages.  It seems to be the case that a pending tree never exists when a commit
is aborted, otherwise strangeness would ensue already since nothing in the
commit abort flow updates the pending tree.  Enne, is that a safe assumption?

+  SetSentScrollDelta(gfx::Vector2dF());
 }
 
 void LayerImpl::ApplyScrollDeltasSinceBeginMainFrame() {
   // Only the pending tree can have missing scrolls.
   DCHECK(layer_tree_impl()->IsPendingTree());
   if (!scrollable())
     return;
 
   // Pending tree should never have sent scroll deltas.
   DCHECK(sent_scroll_delta().IsZero());
@@ skipping 1162 matching lines @@
 
 void LayerImpl::NotifyAnimationFinished(
     base::TimeTicks monotonic_time,
     Animation::TargetProperty target_property,
     int group) {
   if (target_property == Animation::ScrollOffset)
     layer_tree_impl_->InputScrollAnimationFinished();
 }
 
 }  // namespace cc